Stone grinding is a process to restore your ski base to like-new or better than new condition. The ski base surface will have micro damage from normal use, scratches, and heating from an iron. Over time, abrasive snow, drying of the base, wear at high pressure points and application of flouro waxes will eventually seal the base.
Stone grinding will remove a micro layer of old p-tex base and expose newly structured base. It will also help to flatten the base for better glide and easier application and scraping of wax.